Structures for connecting mutually adjacent turbine moving blades include an integral cover-blade structure that has connection covers (integral covers) integrally formed with blades and extending in a circumferential direction on the suction and pressure sides of the blades, and that connects blades by bringing the integral covers on the suction and pressure sides of mutually adjacent blades into contact. Such a blade connection structure has advantages in that the integral covers formed integrally with blades offers a superior resistance (strength) to centrifugal force and the like, and that friction at contact-connecting portions between integral covers provides a large vibration attenuation, thereby allowing a high-reliability blade connection structure to be provided.
An example of a conventional art of a turbine moving blade having an integral cover at the tip of blade is disclosed in Japanese Unexamined Patent Application Publication No. 5-98906. This patent document set forth a structure wherein the integral cover has a pair of suction and pressure sloped side-surfaces inclined relative to the direction of the rotational axis of a turbine, wherein the circumferential pitch of the suction and pressure side surfaces is made larger than the pitch that is obtained by dividing the circumference at a radial position of cover installation by the number of blades over the entire circumference (hereinafter, the latter pitch is referred to as a “geometric pitch”), and wherein the blades are torsionally deformed by being pressed along the circumferential direction of the turbine for assembly, thereby restraining a reaction force against it to strongly connect mutually adjacent blades.
When assembling blades having these integral covers by pressing the blades along the circumferential direction, since the pitch of the covers in the circumferential direction is made larger than the geometric pitch, a reaction force inevitably occurs in the covers. As a result, the blade located at the end position of the train of blades in the process of being assembled (hereinafter, such a blade is referred to as an “end blade”) is subjected to a reaction force only on either one of the suction sloped surface and pressure sloped surface. Hence, the end blade attempts to leave an adjacent blade in the direction away from the adjacent blade, that is, in a manner such that the circumferential component of the reaction force acting on the contact surface becomes weak. This makes the assembly of the blades difficult. In particular, for the blade having high stiffness and small blade length, the reaction force acting along the circumferential direction is large, and therefore, when only the blade root is fixed by friction between a blade root hook and a disk groove, the suction and pressure sloped surfaces of the integral cover of an end blade, respectively located on the suction and pressure sides of adjacent blades, are subjected to forced displacement, resulting in bending deformation of the blade. Consequently, a high stress acts on the basal portion between the cover portion and blade portion. In addition, due to a circumferential force component corresponding to the bending deformation, the blades are bending-deformed in the direction opposite to the direction to assemble blade. This not only makes the assembling of blades difficult but also produces nonuniform contact between the blade root hook and disk groove, thereby causing a high stress therebetween. The blade root hooks and disk grooves support large centrifugal forces acting on the blades during rotation of the turbine. Therefore, when the turbine is rotated at a high speed with a high stress acted on at the time of assembling, strength problem might occur.
Accordingly, the object of this invention is to provide a turbine moving blade capable of being easily assembled, reducing a stress produced at the basal portion between an integral cover and a blade portion, and suppressing nonuniform contact of the engagement portion between the blade root portion and the disk.